For what it’s worth, I’ve just confirmed the current behavior of the “Up/Menu” button on my own personal Fenix 5 (middle button on the left side of the watch), testing it within an app, as well as from the watch face/default watch screen. It behaves as follows, which I hope is what you would expect is the “fixed” or correct behavior.

Within an app:

short-press: UP within an app.

long-press: Brings up MENU within that same app (did NOT bring up the Garmin system menu).

The only time I could get a long-press of the UP/Menu button to bring up the system menu was when the watch was in “watch face” mode, NOT running an app.

If you are able to somehow make the legacy Garmin app available for the Fenix 5 again, I’d be 1) incredibly grateful, and 2) happy to help with beta testing or feedback of any kind.

Oh, and I would also NOT expect any continued support or help with bugs, given that you’ve already stated you’re moving away from the Garmin platform.

Thanks again for the excellent resource/platform that RaceQS provides!